feat: Generic SecretMetadata

[lwin-kyaw]

Explanation

Current metadata class (SeedPhraseMetadata) can only support the Mnemonics type (bytes).
This PR adds additional information to the metadata class so that it can support other types of Secrets with different Data types (besides Uint8Array).
The version field is also added to make sure that the PR addresses the backward/forward compatibility.

References

Changelog

• renamed file and class, SeedPhraseMetadata to SecretMetadata
• added new fields to the SecretMetadata class
  • type (Type of the Secret data, e.g. Mnemonic, PrivateKey
  • version (Version of the SecretMetadata data structure)
• update data field to Generic type which supports Uint8Array, string and number. The reason for it is to make the easier type updates in the future.

Checklist

• I've updated the test suite for new or updated code as appropriate
• I've updated documentation (JSDoc, Markdown, etc.) for new or updated code as appropriate
• I've communicated my changes to consumers by updating changelogs for packages I've changed, highlighting breaking changes as necessary
• I've prepared draft pull requests for clients and consumer packages to resolve any breaking changes

[chaitanyapotti]

lgtm